The latest iteration of Panda, the 4th update reportedly released on June 16, as widely anticipated, addressed the problem of scraper sites which are outranking original authors. Scraper sites are websites that obtain content from other URLs on the web and republish it to their own websites. Webmasters have the same opinion that this update was aimed to identify and penalize spammers.
The official percentage of affected sites was not available, although there have been reports of a huge number of websites which dropped in rankings on Google search engine result pages.
Prior to this, Google implemented a minor Panda update last May 10.